/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package opennlp.maxent;

import maxEntClassifier.MaxEntClassifier;
import maxEntClassifier.R;
import opennlp.model.AbstractEventStream;
import opennlp.model.Event;

/**
 * A object which can deliver a stream of training events assuming that each
 * event is represented as a separated list containing all the contextual
 * predicates, with the last item being the outcome. The default separator is
 * the space " ". e.g.:
 * 
 * <p>
 * cp_1 cp_2 ... cp_n outcome
 * <p>
 * cp_1,cp_2,...,cp_n,outcome
 * 
 * @author Jason Baldridge
 * @version $Revision: 1.5 $, $Date: 2010/09/06 08:02:18 $
 */
public class BasicEventStream extends AbstractEventStream {
	ContextGenerator cg;
	DataStream ds;
	Event next;

	private String separator = " ";

	public BasicEventStream(DataStream ds, String sep) {
		separator = sep;
		cg = new BasicContextGenerator(separator);
		this.ds = ds;
		if (this.ds.hasNext())
			next = createEvent((String) this.ds.nextToken());
	}

	public BasicEventStream(DataStream ds) {
		this(ds, " ");
	}

	/**
	 * Returns the next Event object held in this EventStream. Each call to
	 * nextEvent advances the EventStream.
	 * 
	 * @return the Event object which is next in this EventStream
	 */
	public Event next() {
		while (next == null && this.ds.hasNext())
			next = createEvent((String) this.ds.nextToken());

		Event current = next;
		if (this.ds.hasNext()) {
			next = createEvent((String) this.ds.nextToken());
		} else {
			next = null;
		}
		return current;
	}

	/**
	 * Test whether there are any Events remaining in this EventStream.
	 * 
	 * @return true if this EventStream has more Events
	 */
	public boolean hasNext() {
		while (next == null && ds.hasNext())
			next = createEvent((String) ds.nextToken());
		return next != null;
	}

	private Event createEvent(String obs) {
		int lastSpace = obs.lastIndexOf(separator);
		if (lastSpace == -1)
			return null;

		return new Event(obs.substring(lastSpace + 1), cg.getContext(obs
					.substring(0, lastSpace)));
	}

}
